MR imaging of familial basilar impression.

Basilar impression was found in three members of one family. The mother showed an asymptomatic deformity, her eldest son complained of headache, drop-attacks, nystagmus, unilateral ophthalmoplegia, and ataxia; the middle son presented with headache, nystagmus, and hemiparesis. Magnetic resonance (MR) imaging demonstrated convexobasia of various degrees with elevation of the upper spine and malformation of the occipital bone. The medulla oblongata and the pons were flattened and dislocated backward in two cases. Chiari malformation was present in one case and mild hydrocephalus in another. A comparison of MR with CT imaging demonstrates some advantages of the former method in the assessment of the neural structures directly involved in basilar impression.